Trainline offers two types of insurance: Trainline Protect Travel Insurance (provided by ERGO) and Cancel for Any Reason  (provided by Companjon). The process for making a claim depends on the insurance you selected at the time of booking. 

If you're unsure which insurance you chose, please check your email; they should have sent you a confirmation on the day of your booking.

To make a claim with Cancel for Any Reason
To make a claim with Trainline Protect Travel Insurance